Nearly a third of Mexican adults (32.8 percent) are considered obese—people aged 20 and older whose body mass index (BMI) is 30 and above. That edges out the United States, where 31.8 percent of American adults are considered obese.

Syria at 31.6 percent, is the third fattest among developed countries, while Venezuela and Libya are tied for fourth at 30.8 percent.

Mexico's urban lifestyle and rising income levels coupled with malnourishment among the country's poor have helped it claim this unhealthy title.

“The same people who are malnourished are the ones who are becoming obese,” Abelardo Avila, a physician with Mexico's National Nutrition Institute, told the Global Post. “In the poor classes we have obese parents and malnourished children. The worst thing is the children are becoming programmed for obesity. It's a very serious epidemic.”

Diabetes kills an estimated 70,000 people a year in Mexico—"or roughly equal to the deaths authorities say are caused by more than six years of the country's gangland wars," the Post noted.

About 12 percent of the world's total population is obese, according to the U.N. report.

The world's fattest nation overall is Nauru, a South Pacific island where a staggering 71.1 percent of its 10,000 inhabitants are obese.

The U.N. report does not include data for American Samoa, which has been tabbed in the past as the world's fattest country. According to a 2010 World Health Organization report, nearly all of that Pacific island's inhabitants (95 percent) are considered overweight.

On the other end of the scale is Japan, the thinnest developed country. Just 4.5 of Japanese adults are considered obese, the U.N. says.

Prevalence of obesity among adults in developed countries (% obese)

Rank

Country

Rate

1

Mexico

32.8

2

United States

31.8

3

Syria

31.6

4

Venezuela

30.8

4

Libya

30.8

6

Trinidad & Tobago

30.0

7

Vanuatu

29.8

8

Iraq

29.4

8

Argentina

29.4

10

Turkey

29.3

11

Chile

29.1

12

Czech Republic

28.7

13

Lebanon

28.2

14

New Zealand

27.0

14

Slovenia

27.0

16

El Salvador

26.9

17

Malta

26.6

18

Panama

25.8

18

Antigua

25.8

20

Israel

25.5

21

Australia

25.1

21

Saint Vincent

25.1

22

Dominica

25.0

23

United Kingdom

24.9

23

Russia

24.9

25

Hungary

24.8

Source: United Nations Food and Agricultural Organization's 2013 State of Food and Agriculture Report